EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Laser powder bed fusion provides valuable prospects for nickel-based superalloys that are used in many applications e.g. aerospace, automotive, chemical, and nuclear industries. However, the microstructure and mechanical properties of these materials are especially sensitive to the manufacturing conditions and post-treatment that are applied to relieve the internal stresses, as they are susceptible to the formation of secondary phase precipitates. Generally, a two-step annealing is performed to obtain the desired microstructure. However, the presence of the residual stresses in the as-built samples requires additional stress-relief treatments.
A combination of in situ high-temperature neutron diffraction and synchrotron X-ray diffraction was used to study the evolution of the residual stresses and precipitation in nickel based Alloy 718 for a temperature range from 600°C to 1000°C. Samples with cylindrical symmetry were prepared and by using the 2-bank detector system at the Engin-X beamline, ISIS UK, it was possible to follow the evolution of residual stresses. Rietveld analysis of the X-Ray diffraction data was used to evaluate the initial phase composition and its evolution during the annealing. These results allow for the optimisation of the annealing treatments to relieve residual stresses and, in the meantime, control the microstructure and tense the mechanical properties of the final material.